Wafer chuck, method for producing the same, and  exposure apparatus

ABSTRACT

A wafer chuck includes a base made of a ceramic containing silicon carbide. The base has an oxidation-treated layer, and a film made of diamond-like carbon (DLC) is formed on an outermost surface of the base.

BACKGROUND OF THE INVENTION Field of the Invention

The disclosure relates to a wafer chuck member used to support asubstrate in a lithography process step of producing a semiconductordevice or the like.

Description of the Related Art

It is known that ceramic materials, such as silicon carbide ceramics andsilicon nitride ceramics, are used as wafer chuck members used tosupport a substrate in a lithography process step of producing asemiconductor device. Among them, silicon carbide ceramics are resistantto durability degradation due to their high mechanical strength and havea smaller decrease in the positioning accuracy of a semiconductor wafercaused by a temperature change due to their high thermal conductivity.Thus, silicon carbide ceramics are suitable for wafer chuck members.When a silicon carbide member is ground or polished in a predeterminedshape to be used as a wafer chuck material, however, it is known thatfine microcracks appear on its surface, and fine silicon carbide ceramicparticles separate as dusts from the fine microcracks. Such dusts(wastes) deposited on circuitry of a semiconductor device cause acircuit insulation failure, a short circuit, or another disadvantage.

Thus, it is known that a polycrystalline diamond film or a hard carbonfilm is formed on a surface of a wafer chuck to prevent dusting from thewafer chuck (Japanese Patent Laid-Open No. 6-204324).

In silicon carbide ceramics for use in motor components, it is alsoknown that heat treatment at a temperature in the range of 400° C. to1400° C. in the air or in an oxidizing atmosphere can reduce dusting(Japanese Patent Laid-Open No. 2002-47078). This is because heattreatment in the air or in an oxidizing atmosphere forms a surface filmcontaining an oxide.

However, dusting is reduced only on a wafer chuck surface on which apolycrystalline diamond film or a hard carbon film is formed, anddusting cannot be reduced on a side surface or a back surface on whichsuch a film is not formed.

Heat treatment of a silicon carbide ceramic at a temperature in therange of 400° C. to 1400° C. in the air or in an oxidizing atmospherecan reduce dusting. A surface film containing an oxide thus formed,however, has lower mechanical strength and a higher friction coefficientthan silicon carbide ceramics. Lower durability of wafer chucks due tolower flatness caused by wear as well as dusting caused by wear aredisadvantageous in members that require flatness on the order ofnanometers, such as members for wafer chucks, though these are not greatdisadvantages in motor components. Although silicon carbide ceramicmembers have high wear resistance, sliding on wafer members for extendedperiods causes wear and compromises positioning accuracy or exposureperformance, such as resolution.

SUMMARY OF THE INVENTION

A first aspect of the disclosure provides a wafer chuck comprising abase made of a ceramic containing silicon carbide, wherein the base hasan oxidation-treated layer, and a film made of diamond-like carbon (DLC)is formed on its outermost surface of the base.

A second aspect of the disclosure a method of producing a wafer chuckcomprises oxidation-treating a surface of a base made of a ceramiccontaining silicon carbide, and forming a film made of diamond-likecarbon (DLC).

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a film-forming apparatus according to theembodiment.

FIG. 2A is a schematic view of a wafer chuck according to theembodiment.

FIG. 2B is a schematic view of a wafer chuck according to theembodiment.

FIG. 3A is a schematic view of a wafer chuck according to theembodiment.

FIG. 3B is a schematic view of a wafer chuck according to theembodiment.

FIG. 3C is a schematic view of a wafer chuck according to theembodiment.

FIG. 4 is a schematic view of a lithography process in an exposureapparatus according to the embodiment.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the disclosure are more specifically described below.

A wafer chuck is a member that holds a semiconductor wafer in alithography process apparatus of a semiconductor device. A wafer chuckhas projecting pin portions tens to hundreds of micrometers in heightand diameter formed at intervals of hundreds of micrometers to a fewmillimeters on a surface of the wafer chuck with which a semiconductorwafer comes into contact. The wafer chuck also has holes and grooves foradsorbing the semiconductor wafer.

FIGS. 2A and 2B are schematic views of a wafer chuck for use in theembodiment. FIG. 2A is a top view, and FIG. 2B is a side view. A waferchuck 21 has suction holes 22 passing through the wafer chuck 21 in thethickness direction. The suction holes 22 are used to suck a wafer (notshown), such as a silicon wafer. Although twenty-seven radially arrangedsuction holes 22 are illustrated in the figure, the size, number, andarrangement of the suction holes 22 may be adjusted to appropriatelysuck and fix a wafer on the chuck 21. After the completion of thelithography process of a wafer fixed to the chuck 21, the suction of thewafer is stopped, and lift pins (not shown) are raised through lift pinholes 23 from the back side of the chuck 21 to separate the wafer fromthe chuck 21. Although three circumferentially arranged lift pin holes23 are illustrated in the figure, the size, number, and arrangement ofthe lift pin holes 23 may be adjusted to appropriately separate a waferfrom the chuck 21. A silicon wafer is held on a top surface 24 of thewafer chuck 21. The projecting pin portions (not shown) are formed onthe top surface 24. The wafer chuck 21 can be fixed to a wafer stage viaa flange 25 of the wafer chuck 21.

FIGS. 3A to 3C are schematic views of a diamond-like carbon film and anadhesive layer formed on a base. Projecting pin portions 32 are formedon a base 31. FIGS. 3A to 3C schematically illustrate the shape of thepin portions 32, and the height and width of the pin portions 32 and thedistance between the pin portions 32 are not illustrated to scale.Correctly, as described above, pin portions typically have a height anda diameter of tens to hundreds of micrometers and are arranged atintervals of hundreds of micrometers to a few millimeters. In theembodiment, as illustrated in FIG. 3B, a film (diamond-like carbon film)33 made of diamond-like carbon (DLC) can be formed on the entire frontsurface of the base 31 (the top surface, side surfaces, and bottomsurface of the pin portions). Furthermore, in the embodiment, asillustrated in FIG. 3C, an adhesive layer 34 and the diamond-like carbonfilm 33 can be formed on the front surface of the base 31 in this order.Thus, the film made of diamond-like carbon (DLC) is formed on theoutermost surface of the wafer chuck.

FIG. 4 is a schematic view of a lithography process in an exposureapparatus, which is an example of an apparatus including a wafer chuckaccording to the embodiment. In the figure, an exposure light source 41may be a mercury lamp, a laser source, such as KrF laser or ArF laser,or an X-ray light source. A condenser lens 42 can convert divergentlight from the light source 41 into parallel light. A mask 43 has adesired circuit pattern of a wafer drawn on the surface of a quartzmember or the like. A reduction projection lens 44 can reduce thecircuit pattern drawn on the mask 43 and project it on a wafer 45. Thewafer 45 may be made of silicon. The desired circuit pattern is drawn ona photoresist applied to the surface of the wafer 45 in the lithographyprocess. A wafer chuck 46 is placed on a wafer stage (not shown) and cansupport the wafer 45, such as a silicon wafer. The wafer 45 and thewafer chuck 46 can be successively moved by the wafer stage, and thewafer 45 can be repeatedly exposed to a circuit pattern. In theschematic view of FIG. 4, the circuit pattern is formed in thelithography process using the light source (light). A wafer chuckaccording to the embodiment, however, may also be used in a process oftransferring a micropattern of tens of nanometers or less by pressing anoriginal mold, for example, in a nanoimprint process.

A wafer chuck according to the embodiment in an exposure apparatus canreduce dusting and improve durability by reducing wear.

The base used in the wafer chuck according to the present embodiment canhave a specified shape, for example, by forming a ceramic materialcontaining silicon carbide in a pin shape on a surface of the waferchuck with which a semiconductor wafer comes into contact.

A ceramic containing silicon carbide used in the embodiment is asintered body or polycrystal of silicon carbide. A dense sintered bodycan be formed by using beryllium (Be), boron (B), aluminum (Al), and/ora compound (carbide, nitride, oxide) thereof as a sintering aid inaddition to the silicon carbide component. A silicon carbide polycrystalcan be formed by a chemical vapor deposition (CVD) method. Morespecifically, for example, a single body of a polycrystalline siliconcarbide member can be produced by forming a silicon carbide polycrystala few millimeters in thickness from silicon tetrachloride gas andmethane gas on a graphite base by a thermal CVD method and removing thegraphite base by cutting or by vaporization at high temperature.Containing no sintering aid, the polycrystalline silicon carbide memberformed by the CVD method has higher purity than sintered bodies and hashigh adhesiveness to a diamond-like carbon film to be formed. Thepolycrystalline silicon carbide member is suitable for a wafer chuckmember due to its high mechanical strength and thermal conductivity.Sintered bodies composed mainly of silicon carbide and polycrystallinesilicon carbide members formed by the CVD method are referred to asceramics containing silicon carbide (silicon carbide ceramics) in theembodiment.

A wafer chuck should have high flatness particularly in pin-shapedportions on a surface of the wafer chuck with which a semiconductorwafer comes into contact. When a base is ground or polished in apredetermined shape, fine microcracks appear on its surface, and finesilicon carbide ceramic particles separate as dusts (wastes) from thefine microcracks. Such dusts deposited on circuitry of a semiconductordevice sometimes cause a circuit insulation failure or a short circuit.

To solve the disadvantages, in the present embodiment, a surface of abase made of a ceramic containing silicon carbide is first subjected tooxidation treatment. More specifically, for example, the base is heatedat a temperature in the range of 300° C. to 700° C. in the air or in anoxygen atmosphere for tens of minutes to tens of hours. This oxidizes amicrocrack portion on the surface and forms a film containing an oxide(an oxidation-treated layer). The film containing an oxide(oxidation-treated layer) has a thickness in the range of approximately1 to 100 nm. The oxygen atom concentration in the film containing anoxide (oxidation-treated layer) is more than 25 atomic percent. Theoxygen atom concentration in the film can be measured with an elementalanalyzer of an electron microscope. The oxygen atom concentration of theoxidation-treated layer tends to increase with treatment temperature andtreatment time.

Ceramic materials containing silicon carbide typically have high thermalstability and are rarely oxidized at a temperature in the range ofapproximately 300° C. to 700° C. A microcrack portion formed by grindingor polishing, however, has high reactivity due to a defect or distortioncaused by the processing and may be easily oxidized at low temperatures.A film containing an oxide formed in a microcrack portion increases thevolume of a crack surface portion and covers the microcrack portion,thereby reducing the separation of fine particles from the surface. Ahigher oxidation treatment temperature typically results in a thickerfilm containing an oxide and a higher anti-dusting effect. An oxidationtreatment temperature of, for example, 1000° C. or more, however,sometimes causes thermal deformation and results in a wafer chuck withinsufficient flatness. Thus, it is desirable that the oxidationtreatment temperature be as low as 300° C. to 700° C. and the treatmenttime be longer (desirably a few hours or more). The optimum oxidationtreatment conditions for a ceramic sintered body containing siliconcarbide depend on the particle size before sintering, the sinteringstate, the type of sintering aid, and the grinding or polishingconditions. Thus, these conditions are appropriately controlled. Theoptimum oxidation treatment conditions for a polycrystalline siliconcarbide member formed by the CVD method also depend on the averageparticle size of the polycrystal and the grinding or polishingconditions. Thus, these conditions are also appropriately controlled.

After the oxidation treatment, a film made of diamond-like carbon (DLC)(a diamond-like carbon film) is formed.

It is known that diamond-like carbon films are typically coatingmaterials that have high film stress and are easily separated, butdiamond-like carbon films have relatively high adhesiveness to siliconcarbide members.

In ceramic sintered bodies containing silicon carbide, however, anoxidized layer is formed on the surface of the sintering aid undercertain oxidation treatment conditions. This sometimes causes thedisadvantages of poor adhesion between a diamond-like carbon film and aceramic member containing silicon carbide and the separation of thediamond-like carbon film. This is because the sintering aid material ismore easily oxidized than silicon carbide materials. Thus, also toimprove the adhesiveness of a diamond-like carbon film, it is desirablethat the oxidation treatment temperature be as low as 300° C. to 700° C.Under these oxidation treatment conditions, the amount of sintering aidin a ceramic sintered body containing silicon carbide is generally assmall as a few percent or less by weight, and the adhesiveness to adiamond-like carbon film is at a practical level.

A polycrystalline silicon carbide member formed by the CVD method, whichcontains no sintering aid, is free from oxidation of the sintering aidportion and has a smaller decrease in adhesiveness to a diamond-likecarbon film resulting from oxidation treatment. This is probably becausethe oxidation of a crack portion in oxidation treatment is mainly causedby a reaction within silicon carbide crystal grains, and a surfaceportion with which a diamond-like carbon film comes into contact rarelyhas an oxidized portion. Also in this respect, the polycrystallinesilicon carbide member formed by the CVD method is suitable for thebase.

After the formation of a layer containing at least silicon or carbon, adiamond-like carbon film can be formed on the layer containing at leastsilicon or carbon to improve adhesiveness. In other words, a layercontaining at least silicon or carbon and a film made of diamond-likecarbon (a diamond-like carbon film) can be sequentially stacked.

After the formation of an amorphous layer containing carbon, silicon,oxygen, and hydrogen, a diamond-like carbon film can also be formed onthe amorphous layer containing carbon, silicon, oxygen, and hydrogen toimprove adhesiveness. In other words, an amorphous layer containingcarbon, silicon, oxygen, and hydrogen and a diamond-like carbon film canbe sequentially stacked.

The layer containing at least silicon or carbon or the amorphous layercontaining carbon, silicon, oxygen, and hydrogen is referred to as anadhesive layer. The adhesive layer is formed to further improve adhesionbetween a silicon carbide ceramic member and a diamond-like carbon film.

A layer containing at least silicon or carbon in the embodiment includesa silicon film, a silicon nitride film, or a carbide film, such as asilicon carbide film or a carbon nitride film. Although the layercontaining at least silicon or carbon may contain oxygen, the oxygencontent is 25 atomic percent or less, desirably 20 atomic percent orless.

The amorphous layer containing carbon, silicon, oxygen, and hydrogen issuitable for an adhesive layer due to its high adhesiveness to adiamond-like carbon film and small film stress. Each of the carbon,silicon, oxygen, and hydrogen atom concentrations in the film can be 5atomic percent or more, and the oxygen atom concentration can be 20atomic percent or less. The concentration of each element in the filmcan be measured with an elemental analyzer of an electron microscope.

FIG. 1 illustrates a film-forming apparatus for forming the adhesivelayer and a diamond-like carbon film. The film-forming apparatusillustrated in FIG. 1 is a high-frequency plasma chemical vapordeposition (CVD) apparatus. A film-forming apparatus used in the presentembodiment is not limited to this, and a known ion plating apparatus orsputtering apparatus may also be used. Although the film-formingapparatus in the present embodiment can successively form the adhesivelayer and a diamond-like carbon film, the adhesive layer and thediamond-like carbon film may be formed with different apparatuses. Forexample, the adhesive layer may be formed with a high-frequency plasmaCVD apparatus as illustrated in FIG. 1, and a diamond-like carbon filmmay be formed with another apparatus, such as an ion plating apparatus,a sputtering apparatus, or a cathode arc film-forming apparatus.Alternatively, after the adhesive layer is formed with a sputteringapparatus, a diamond-like carbon film may be formed with thehigh-frequency plasma CVD apparatus illustrated in FIG. 1.

In FIG. 1, a vacuum chamber 1 is equipped with a vacuum pump (not shown)and a vacuum valve (not shown) and can be evacuated to 1×10⁻³ Pa. Aground electrode 2 also serving as a raw material gas introductionshowerhead has many openings approximately 1 mm in diameter on itsbottom surface in the figure. The raw material gas can be introducedthrough the openings. The diameter and pitch of the openings areappropriately determined to make the thickness distribution of a film tobe formed uniform. The ground electrode 2 also serving as a raw materialgas introduction showerhead is also used as a ground electrode. A rawmaterial gas inlet 3 is coupled to a gas valve, a gas flow controller,and a raw material gas cylinder (all not shown).

To form an amorphous layer containing carbon, silicon, oxygen, andhydrogen with the apparatus, for example, a liquid organosiliconcompound can be used as a raw material gas. The liquid organosiliconcompound can be used by heating tetraethoxysilane orhexamethyldisiloxane (for example, approximately 40° C.) forgasification. These gases may also be diluted with a noble gas (argongas, helium gas, etc.), nitrogen gas, or hydrogen gas.

Various carbon-containing gases and liquid organic compounds subjectedto vaporization can be used as raw material gases for a diamond-likecarbon film. Examples of the carbon-containing gases include hydrocarbongases, such as methane, ethane, ethylene, and acetylene, carbonmonoxide, and halogenated carbons. Examples of the liquid organiccompounds include alcohols, such as methanol and ethanol, ketones, suchas acetone, aromatic hydrocarbons, such as benzene and toluene, ethers,such as dimethyl ether, and organic acids, such as formic acid andacetic acid. These gases may also be diluted with a noble gas (argongas, helium gas, etc.), nitrogen gas, or hydrogen gas. A base 4 isproduced by processing a base made of a ceramic containing siliconcarbide in a specified shape and subjecting the base to the oxidationtreatment. The base 4 can be placed on a high-frequency introductionelectrode 5 also serving as a substrate holder. The high-frequencyintroduction electrode 5 can also be used to apply high-frequency power.A high-frequency power supply 6 supplies high-frequency power to thehigh-frequency introduction electrode 5 also serving as a substrateholder.

To form a film containing at least silicon as an adhesive layer, forexample, a silicon target can be sputtered by a known sputtering methodto form a silicon film. A gas mixture of argon and nitrogen can be usedas a sputtering gas to form a silicon nitride film. A silicon carbidetarget can also be sputtered to form a silicon carbide film.

In the amorphous layer containing carbon, silicon, oxygen, and hydrogenused as an adhesive layer, each of the carbon, silicon, oxygen, andhydrogen atom concentrations is at least 5 atomic percent. The oxygenatom concentration is 20 atomic percent or less. The amorphous layercontaining carbon, silicon, oxygen, and hydrogen is also referred to asa C—Si—O—H film. Incidental impurities in the formation of the film maybe approximately 1 atomic percent or less of a diluent gas, such asnitrogen or argon, or a metallic element of the chamber and substrateholder, such as iron or aluminum. The amorphous layer containing carbon,silicon, oxygen, and hydrogen in the present embodiment is formedbetween the ceramic base containing silicon carbide and a diamond-likecarbon film and is used as an intermediate layer to improveadhesiveness. Carbon and silicon in the layer improve adhesiveness, andhydrogen and oxygen in the layer reduce film stress and further improveadhesiveness. Adhesiveness is improved at an oxygen atom concentrationof 20 atomic percent or less, and adhesiveness to a diamond-like carbonfilm is sometimes not improved at an oxygen atom concentration of morethan 25 atomic percent. The amorphous layer containing carbon, silicon,oxygen, and hydrogen can be an amorphous film without crystallinity.

The thickness of the adhesive layer can be appropriately adjusted andranges from, for example, 0.01 μm or more and 1 μm or less, desirably0.02 μm or more and 0.4 μm or less.

A film made of diamond-like carbon (DLC) (a diamond-like carbon film) isthus called because it is basically amorphous, has high hardness, andhas high transparency in the infrared region. A film made ofdiamond-like carbon (DLC) (a diamond-like carbon film) is sometimesreferred to as a hard carbon film, an i-C film (i-carbon film), or ata-C film (tetrahedral amorphous carbon film). A film made ofdiamond-like carbon (DLC) (a diamond-like carbon film) is composed onlyof carbon atoms and incidental impurities or contains hydrogen gasgenerated from a raw material. The film containing hydrogen gas issometimes referred to as an a-C:H film. A diamond-like carbon filmaccording to the embodiment includes the a-C:H film. Incidentalimpurities may be approximately 1 atomic percent or less of a diluentgas, such as nitrogen, argon, or atmospheric oxygen, or a metallicelement of the chamber and substrate holder, such as iron or aluminum.The thickness of the film can be appropriately adjusted and ranges from,for example, 0.04 μm or more and 1 μm or less, desirably 0.05 μm or moreand 0.4 μm or less.

EXAMPLES

The disclosure is described in detail in the following exemplaryembodiments.

Evaluation of Amount of Dust

In the present exemplary embodiments, the amount of dust in a waferchuck was evaluated by the following method. A base made of a ceramiccontaining silicon carbide ground in a specified shape was placed on aclean bench, and surrounding air was introduced by suction into aparticle counter to measure dust 0.1 μm or more in size. The amount ofdust was based on the amount of dust in Comparative Example 1, in whicha base made of a ceramic sintered body containing silicon carbide wasnot subjected to oxidation treatment and no adhesive layer and nodiamond-like carbon film were formed. The amounts of dust in theexemplary embodiments and the other comparative examples were compared.

Evaluation of Durability

Durability was evaluated by a pin-on-disk method in a sliding test.

Samples were prepared by grinding a material equivalent to a base madeof a ceramic containing silicon carbide in a flat sheet shape andsubjecting the material to various treatments described in the exemplaryembodiments and comparative examples. While a ϕ8 silicon sphere wasplaced on a sample under a load of 50 g, a test was performed at a widthof 5 mm and at a sliding rate of 1 mm/s. After the test, the slideportion was checked for a sliding wear scar with an optical microscopeor a scanning electron microscope. A sample including a film was checkedfor the separation of the film with an optical microscope or a scanningelectron microscope. The wear scar shape was determined with aninterferometer that can observe the surface profile.

Exemplary Embodiment 1

First, a base made of a ceramic sintered body containing silicon carbideground in a specified shape was placed in a furnace and was subjected tooxidation treatment. The base was heated to 400° C. at a heating rate of10° C./min in the air, was maintained at 400° C. for 5 hours, and wasthen slowly cooled to room temperature over 8 hours. The base made of aceramic sintered body containing silicon carbide was then placed in ahigh-frequency plasma CVD apparatus as illustrated in FIG. 1, which wasevacuated to 1×10⁻³ Pa with a vacuum pump. Argon gas for plasma cleaningwas then introduced into the raw material gas introduction showerhead 2,and the pressure was adjusted to be 5 Pa. High-frequency power was thenapplied from the high-frequency power supply 6 to the substrate holder 5at 450 W to generate plasma, which was used to clean the surface of thebase 4 (to remove water and contamination). The argon gas was thenstopped, and the apparatus was evacuated to 1×10⁻³ Pa with a vacuumpump. Toluene to be used to form a diamond-like carbon film was thenintroduced into the raw material gas introduction showerhead 2, and thepressure was adjusted to be 5 Pa. High-frequency power was then appliedfrom the high-frequency power supply 6 to the substrate holder 5 at 450W to generate plasma. A 100-nm diamond-like carbon film (DLC film) wasformed on the surface of the base 4.

A diamond-like carbon film for analytical evaluation was separatelyformed on a silicon base under the same conditions as in the presentexemplary embodiment. The analysis showed that the diamond-like carbonfilm was composed of carbon and hydrogen at C:H=75.3:24.7 based onatomic percent and had a hardness of 20 GPa.

The amount of dust in the wafer chuck was measured by the abovespecified method. In the same manner as in the present exemplaryembodiment, a ceramic sintered body containing silicon carbide wassubjected to oxidation treatment, and a diamond-like carbon film wasformed on the ceramic sintered body to prepare a ϕ60 flat sheet sample.The flat sheet sample was examined by the pin-on-disk method in thesliding test. After the test, the flat sheet sample was checked for asliding wear scar and film separation with an optical microscope and ascanning electron microscope. Table 1 shows the evaluation results.

Exemplary Embodiment 2

A base made of polycrystalline silicon carbide formed by the CVD methodground in a specified shape was subjected to oxidation treatment in afurnace. The base was heated to 450° C. at a heating rate of 5° C./minin the air, was maintained at 450° C. for 10 hours, and was then slowlycooled to room temperature over 12 hours. The base made ofpolycrystalline silicon carbide formed by the CVD method was then placedin a high-frequency plasma CVD apparatus as illustrated in FIG. 1, whichwas evacuated to 1×10⁻³ Pa with a vacuum pump. Argon gas for plasmacleaning was then introduced into the raw material gas introductionshowerhead 2, and the pressure was adjusted to be 5 Pa. High-frequencypower was then applied from the high-frequency power supply 6 to thesubstrate holder 5 at 450 W to generate plasma, which was used to cleanthe surface of the base 4. Toluene to be used to form a diamond-likecarbon film was then introduced into the raw material gas introductionshowerhead 2, and the pressure was adjusted to be 5 Pa. High-frequencypower was then applied from the high-frequency power supply 6 to thesubstrate holder 5 at 600 W to generate plasma. A 150-nm diamond-likecarbon film (DLC film) was formed on the surface of the base 4.

A diamond-like carbon film for analytical evaluation was separatelyformed on a silicon base under the same conditions as in the presentexemplary embodiment. The analysis showed that the diamond-like carbonfilm was composed of carbon and hydrogen at C:H=80.5:19.5 based onatomic percent and had a hardness of 22 GPa.

The amount of dust in the wafer chuck was measured by the abovespecified method. In the same manner as in the present exemplaryembodiment, a diamond-like carbon film was formed on a ϕ60 flat sheetsample made of the CVD polycrystalline silicon carbide to prepare asample. The flat sheet sample was examined by the pin-on-disk method inthe sliding test. After the test, the flat sheet sample was checked fora sliding wear scar and film separation with an optical microscope and ascanning electron microscope. Table 1 shows the dusting test and slidingevaluation results.

Exemplary Embodiment 3

First, a base made of a ceramic sintered body containing silicon carbideground in a specified shape was placed in a furnace and was subjected tooxidation treatment. The base was heated to 400° C. at a heating rate of10° C./min in the air, was maintained at 400° C. for 5 hours, and wasthen slowly cooled to room temperature over 8 hours. The base made of aceramic containing silicon carbide was placed in a high-frequency plasmaCVD apparatus as illustrated in FIG. 1, which was evacuated to 1×10 Pawith a vacuum pump. Argon gas for plasma cleaning was then introducedinto the raw material gas introduction showerhead 2, and the pressurewas adjusted to be 5 Pa. High-frequency power was then applied from thehigh-frequency power supply 6 to the substrate holder 5 at 450 W togenerate plasma, which was used to clean the surface of the base 4. Toform an amorphous layer containing carbon, silicon, oxygen, andhydrogen, a raw material gas hexamethyldisiloxane was introduced intothe vacuum chamber 1 through the raw material gas introductionshowerhead 2, and the pressure was adjusted to be 5 Pa. High-frequencypower was then applied from the high-frequency power supply 6 to thesubstrate holder 5 at 450 W to generate plasma. An 80-nm amorphous layercontaining carbon, silicon, oxygen, and hydrogen was formed on thesurface of the base 4. The introduction of hexamethyldisiloxane was thenstopped. After the vacuum chamber 1 was evacuated to 1×10⁻³ Pa with avacuum pump, toluene to be used to form a diamond-like carbon film wasintroduced into the raw material gas introduction showerhead 2. Thepressure was adjusted to be 5 Pa. High-frequency power was then appliedfrom the high-frequency power supply 6 to the substrate holder 5 at 450W to generate plasma. A 100-nm diamond-like carbon film (DLC film) wasformed on the amorphous layer containing carbon, silicon, oxygen, andhydrogen.

An amorphous monolayer containing carbon, silicon, oxygen, and hydrogenand a diamond-like carbon monolayer for analytical evaluation wereseparately formed on a silicon base under the same conditions as in thepresent exemplary embodiment. The analysis showed that the amorphouslayer containing carbon, silicon, oxygen, and hydrogen had a compositionof C:Si:O:H=40.5:13.0:11.1:35.4 based on atomic percent. The analysisalso showed that the diamond-like carbon film was composed of carbon andhydrogen at C:H=75.3:24.7 based on atomic percent and had a hardness of20 GPa.

The amount of dust in the wafer chuck was measured by the abovespecified method. In the same manner as in the present exemplaryembodiment, a ceramic containing silicon carbide was subjected tooxidation treatment, and an amorphous layer containing carbon, silicon,oxygen, and hydrogen and a diamond-like carbon film were formed on theceramic to prepare a ϕ60 flat sheet sample. The flat sheet sample wasexamined by the pin-on-disk method in the sliding test. After the test,the flat sheet sample was checked for a sliding wear scar and filmseparation with an optical microscope and a scanning electronmicroscope. Table 1 shows the evaluation results.

Exemplary Embodiment 4

A base made of a ceramic sintered body containing silicon carbide groundin a specified shape was placed in a furnace, and for oxidationtreatment was heated to 600° C. at a heating rate of 10° C./min in theair, was maintained at 600° C. for 3 hours, and was then slowly cooledto room temperature over 8 hours. The base made of a ceramic sinteredbody containing silicon carbide was then placed in a high-frequencyplasma CVD apparatus as illustrated in FIG. 1, which was evacuated to1×10⁻³ Pa with a vacuum pump. To form an amorphous layer containingcarbon, silicon, oxygen, and hydrogen, raw material gases,hexamethyldisiloxane and argon gas at a ratio of 1:5, were introducedinto the vacuum chamber 1 through the raw material gas introductionshowerhead 2, and the pressure was adjusted to be 6 Pa. High-frequencypower was then applied from the high-frequency power supply 6 to thesubstrate holder 5 at 600 W to generate plasma. A 50-nm amorphous layercontaining carbon, silicon, oxygen, and hydrogen was formed on thesurface of the base 4. The introduction of hexamethyldisiloxane andargon gas was then stopped. After the apparatus was evacuated to 1×10⁻³Pa with a vacuum pump, toluene and argon gas at a ratio of 1:5 to beused to form a diamond-like carbon film was introduced into the rawmaterial gas introduction showerhead 2, and the pressure was adjusted tobe 4 Pa. High-frequency power was then applied from the high-frequencypower supply 6 to the substrate holder 5 at 650 W to generate plasma. A100-nm diamond-like carbon film (DLC film) was formed on the amorphouslayer containing carbon, silicon, oxygen, and hydrogen.

An amorphous layer containing carbon, silicon, oxygen, and hydrogen anda diamond-like carbon film for analytical evaluation were separatelyformed on a silicon base under the same conditions as in the presentexemplary embodiment. The analysis showed that the amorphous layercontaining carbon, silicon, oxygen, and hydrogen had a composition ofC:Si:O:H=35.4:20.6:9.0:35.0 based on atomic percent. The analysis showedthat the diamond-like carbon film was composed of carbon and hydrogen atC:H=78.0:22.0 based on atomic percent and had a hardness of 21 GPa.

The amount of dust in the wafer chuck was measured by the abovespecified method. In the same manner as in the present exemplaryembodiment, a ceramic containing silicon carbide was subjected tooxidation treatment, and an amorphous layer containing carbon, silicon,oxygen, and hydrogen and a diamond-like carbon film were formed on theceramic to prepare a ϕ60 flat sheet sample. The flat sheet sample wasexamined by the pin-on-disk method in the sliding test. After the test,the flat sheet sample was checked for a sliding wear scar and filmseparation with an optical microscope and a scanning electronmicroscope. Table 1 shows the evaluation results.

Comparative Example 1

A base made of a ceramic sintered body containing silicon carbide groundin a specified shape in the same manner as in Exemplary Embodiment 1 wasnot subjected to oxidation treatment, and no adhesive layer and nodiamond-like carbon film were formed on the base. The amount of dust inthe base was measured by the specified method. A ϕ60 flat sheet sampleof a ceramic containing silicon carbide was prepared without oxidationtreatment and without the formation of the adhesive layer and thediamond-like carbon film. The sample was examined by the pin-on-diskmethod in the sliding test. After the test, the sample was checked for asliding wear scar with an optical microscope and a scanning electronmicroscope. Table 1 shows the evaluation results.

Comparative Example 2

In Comparative Example 2, a base made of a ceramic sintered bodycontaining silicon carbide ground in a specified shape in the samemanner as in Exemplary Embodiment 1 was subjected to heat treatment(400° C.) in the same manner as in Exemplary Embodiment 1. No adhesivelayer and no diamond-like carbon film (DLC film) were formed in thepresent comparative example. The amount of dust was measured by thespecified method in the same manner as in Exemplary Embodiment 1. A ϕ60flat sheet sample of a silicon carbide ceramic only subjected tooxidation treatment was prepared and was examined by the pin-on-diskmethod in the sliding test. After the test, the ϕ60 flat sheet samplewas checked for a sliding wear scar with an optical microscope and ascanning electron microscope. Table 1 shows the evaluation results.

TABLE 1 Exemplary Exemplary Exemplary Exemplary Comparative ComparativeEmbodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Example 1 Example 2Chuck Silicon carbide Polycrystalline Silicon carbide Silicon carbideSilicon Silicon carbide member ceramic silicon carbide ceramic ceramiccarbide ceramic sintered body formed by CVD sintered body sintered bodyceramic sintered body method sintered body Oxidation Heat treatment Heattreatment Heat treatment Heat treatment Heat treatment treatment at 400°C. in the at 450° C. in the at 400° C. in the at 600° C. in the at 400°C. in the air air air air air DLC film DLC film DLC film C—Si—O—HC—Si—O—H structure monolayer monolayer (150 intermediate intermediate(100 nm) nm) layer/DLC film layer/DLC film Measured about 1/100 of about1/250 of about 1/250 of about 1/250 of 1 (control) about 1/200 of amountof untreated untreated untreated untreated untreated dust (Comparative(Comparative (Comparative (Comparative (Comparative Example 1)Example 1) Example 1) Example 1) Example 1) Sliding Partial film No filmNo film No film Sliding wear Sliding wear test results separation atseparation separation separation scars scars sintering aid No sliding Nosliding No sliding portion wear scar wear scar wear scar No sliding wearscar except separated portion

Evaluation

Exemplary Embodiments 1 to 4 of the disclosure showed that the amount ofdust was greatly decreased, no sliding wear scar was observed in thesliding test and the sliding durability was good, and the diamond-likecarbon film was not separated. More specifically, in ExemplaryEmbodiment 1, in which the diamond-like carbon film was formed on thewafer chuck made of the ceramic sintering base containing siliconcarbide subjected to oxidation treatment, the amount of dust was greatlydecreased ( 1/100 of Comparative Example 1). Although the diamond-likecarbon film was partly separated in the sintering aid portion in thesliding test, no sliding wear scar was observed in the other portion.Thus, the sliding test was at a practically acceptable level.

Exemplary Embodiment 2 showed that the diamond-like carbon film on thepolycrystalline silicon carbide member formed by the CVD method was notseparated in the sliding test, thus showing good adhesiveness. This isbecause the polycrystalline silicon carbide member formed by the CVDmethod without the sintering aid is more resistant to thermal oxidationtreatment and has higher adhesiveness to the diamond-like carbon filmthan sintered bodies. In the wafer chucks including the base made of theceramic containing silicon carbide sintering, the formation of theadhesive layer (Exemplary Embodiments 3 and 4) further reduces dustingand film separation.

In contrast, in Comparative Example 1, in which the chuck base was notsubjected to oxidation treatment and no adhesive layer and nodiamond-like carbon film were formed, the amount of dust was increased,and a sliding wear scar was observed in the sliding test, whichindicates poor sliding durability. In Comparative Example 2, in whichonly oxidation treatment was performed, the amount of dust was greatlydecreased, but a sliding wear scar was observed in the sliding test,which indicates poor sliding durability.

Exemplary Embodiments 5 and 6

A silicon film or a silicon nitride film was formed as an adhesive layerby a known sputtering method on a ϕ60 flat sheet sample made of apolycrystalline silicon carbide formed by the CVD method subjected toprocessing and oxidation treatment in the same manner as in ExemplaryEmbodiment 1. A diamond-like carbon film was formed in the samples underthe same conditions as in Exemplary Embodiment 3. For these samples, theload condition in the sliding test by the pin-on-disk method was changedto double (100 g). After the test, the samples were checked for asliding wear scar and film separation with an optical microscope and ascanning electron microscope. The evaluation results showed that the twosamples including the silicon film or the silicon nitride film as anadhesive layer had no film separation and no sliding wear scar.

Exemplary Embodiment 7

An amorphous layer containing carbon, silicon, oxygen, and hydrogen wasformed with a high-frequency plasma CVD apparatus as illustrated in FIG.1 as an adhesive layer on a ϕ60 flat sheet sample made of apolycrystalline silicon carbide formed by the CVD method subjected toprocessing and oxidation treatment in the same manner as in ExemplaryEmbodiment 1. A diamond-like carbon film was formed on the sample underthe same conditions as in Exemplary Embodiment 1. For this sample, theload condition of the pin-on-disk method in the sliding test was changedto double (100 g). After the test, the sample was checked for a slidingwear scar and film separation with an optical microscope and a scanningelectron microscope. The evaluation results showed no film separationand no sliding wear scar.

While the present disclosure has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2019-182530, filed Oct. 2, 2019, and Japanese Patent Application No.2020-134003, filed Aug. 6, 2020, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A wafer chuck comprising a base made of a ceramiccontaining silicon carbide, wherein the base has an oxidation-treatedlayer, and a film made of diamond-like carbon (DLC) is formed on anoutermost surface of the base.
 2. The wafer chuck according to claim 1,wherein a layer containing at least silicon or carbon is formed betweenthe oxidation-treated layer and the film.
 3. The wafer chuck accordingto claim 2, wherein the layer containing at least silicon or carbon hasa thickness of 0.01 μm or more and 1 μm or less.
 4. The wafer chuckaccording to claim 2, wherein the layer containing at least silicon orcarbon is a layer composed mainly of silicon, silicon nitride, siliconcarbide, or carbon nitride.
 5. The wafer chuck according to claim 1,wherein an amorphous layer containing carbon, silicon, oxygen, andhydrogen is formed between the oxidation-treated layer and the film. 6.The wafer chuck according to claim 5, wherein the amorphous layercontaining carbon, silicon, oxygen, and hydrogen has a thickness of 0.01μm or more and 1 μm or less.
 7. The wafer chuck according to claim 5,wherein each of carbon, silicon, oxygen, and hydrogen atomconcentrations in the amorphous layer containing carbon, silicon,oxygen, and hydrogen is 5 atomic percent or more, and an oxygen atomconcentration is 20 atomic percent or less.
 8. The wafer chuck accordingto claim 1, wherein the film has a thickness of 0.04 μm or more and 1 μmor less.
 9. The wafer chuck according to claim 1, wherein theoxidation-treated layer has an oxygen atom concentration of more than 25atomic percent.
 10. A method of producing a wafer chuck, comprising:oxidation-treating a surface of a base made of a ceramic containingsilicon carbide; and forming a film made of diamond-like carbon (DLC).11. The method for producing a wafer chuck according to claim 10,further comprising: forming a layer containing at least silicon orcarbon on the oxidation-treated base after the oxidation-treating andbefore the forming the film.
 12. The method for producing a wafer chuckaccording to claim 10, further comprising: forming an amorphous layercontaining carbon, silicon, oxygen, and hydrogen on theoxidation-treated base after the oxidation-treating and before theforming the film.
 13. An exposure apparatus comprising the wafer chuckaccording to claim 1.